The present invention relates generally to a planisphere timepiece that may visually display sidereal time and/or solar time.
Time may be measured in different ways. Sidereal time, also known as “star time”, is the measurement of time based on the apparent motion of the stars due to the rotation of the earth or any other celestial body. A sidereal day lasts from when a distant star appears on an observer's celestial meridian until it next appears on the observer's celestial meridian. Sidereal time is useful in the field of astronomy. For example, star coordinates are often written in sidereal time. In particular, sidereal time equals the right ascension of any point on the celestial sphere of the sky that crosses a meridian at a given moment. For this reason, sidereal time may be used by astronomers and backyard stargazers alike to determine which astronomical objects may be visible at a given time.
Unlike sidereal time, solar time, which is also commonly referred to as “local time,” is based on the apparent movement of the sun relative to Earth. In particular, solar time is based on the sun's daily crossing of an observer's local longitudinal meridian, which is the 24-hour period tracked by many typical timepieces such as wall clocks and watches. Solar noon is specifically defined as the moment when the sun is at its highest point in the sky, although many timepieces may not accurately reflect solar noon due to time zones and daylight savings time. In addition, the time taken for the sun to return to its highest point is exactly 24 hours, or a solar day. A solar day is slightly longer than a sidereal day (i.e., a sidereal day lasts about 23 hours and 56 minutes).
Primarily for human convenience, local time has evolved into the modern standard of Coordinated Universal Time (i.e., UTC), which has been adopted over longitudinal time zones as a means of standardization. Time zones are based off of a zero UTC hour longitudinal coordinate that runs through Greenwich, England. In the United States, there are four different time zones. The Eastern time zone is five hours behind Greenwich, England, or “−5 UTC,” whereas the Central, Mountain, and Pacific time zones are −6 UTC, −7 UTC, and −8 UTC, respectively.
Celestial planispheres may be useful for determining the position of the stars and constellations. Celestial planispheres are typically an assembly including a rotatable, circular map of the heavens used to locate and identify stars and constellations relative to calendar and local time information. Based on the date, local time, and location of a user, a celestial planisphere may provide the user with a map view of the stars and other astronomical features that may be found in the sky.
A celestial planisphere must be calibrated in order to provide accurate information. In particular, since sidereal time varies depending on the longitudinal position on the Earth as well as the local time and date, there is a need to be able to calibrate a celestial planisphere to the user's particular geographic location to ensure that the planisphere is accurate. In addition, there is a need for a celestial planisphere that may provide an indication of sidereal time. Moreover, in light of the differences between sidereal time and local time, there is a need for a celestial planisphere that may provide sidereal time in addition to local time. Such needs are also applicable to other types of planispheres including, but not limited to, terrestrial planispheres.
In light of the aforementioned needs, it may be desirable to have a clock that displays a planisphere and both sidereal time and local time. It may also be desirable to have a clock that not only displays the entire planisphere, but may accurately identify for the user which part of the planisphere may be visible to a user at a given time. In addition, it may be desirable to have a clock that a user may adjust relative to his or her geographic location for accuracy.
One exemplary embodiment of the present invention may be a clock, watch, or other timepiece (e.g., a 24-hour analog timepiece) that includes a planisphere and sidereal time information. An exemplary embodiment of a timepiece may include an adjustment feature that allows a user to adjust the face of the timepiece so that it is accurate for the user's geographic location and/or local time. An exemplary embodiment of the present invention also includes a system and method for indexing a timepiece to take geographic location and/or local time variations into account. Furthermore, another exemplary embodiment of the present invention includes a system and method for providing sidereal time. For example, an exemplary embodiment of the present invention includes a system and method for adapting an automatic quartz solar time mechanism to provide sidereal time.
In addition to the novel features and advantages mentioned above, other features and advantages of the present invention will be readily apparent from the following descriptions of the drawings and exemplary embodiments.